The field of art to which this invention pertains is oxymethylene polymers.
Oxymethylene polymers which have recurring --CH.sub.2 O-- units have been known for many years. They are prepared by the polymerization of formaldehyde or trioxane which is a cyclic trimer of formaldehyde. Oxymethylene polymers vary in molecular weight depending on the method of preparation.
High molecular weight solid oxymethylene polymers have been prepared by polymerizing trioxane in the presence of certain fluoride catalysts, such as boron trifluoride coordination complexes with organic compounds as described in U.S. Pat. No. 2,989,506. The use of boron trifluoride in its gaseous form is described in U.S. Pat. No. 2,989,507. Oxymethylene copolymers containing repeating carbon-to-carbon single bonds in the polymer chain are prepared by copolymerizing trioxane and any of various cyclic ethers, such as ethylene oxide or dioxolane as disclosed in U.S. Pat. No. 3,027,352. Such copolymers contain from about 85 to about 99.6 mole percent of oxymethylene units interspersed with between about 0.4 and 15 mole percent of --O--R-- units wherein R is a divalent radical containing at least 2 carbon atoms directly linked to each other and positioned in the chain between the two valences with any substituents on the R radical being inert.
Other methods of preparing oxymethylene polymer are disclosed by Kern et. al. in Angewandte Chemie 73 pp. 177-186, (Mar. 21, 1961) including polymers containing repeating carbon-to-carbon single bonds in the polymer chain by copolymerizing trioxane with cyclic ethers, such as dioxane, lactones, such as beta-propiolactone, anhydrides, such as cyclic adipic anhydride and ethylenically unsaturated compounds, such as styrene, vinyl acetate, vinyl methyl ketone, acrolein and the like.
Continuous processes for preparing oxymethylene polymers are described in U.S. Pat. Nos. 4,105,637, 4,115,369, 4,224,435 and 4,431,794.